What Kinds of Chemicals Are in Paint?

Paint is a coating material made by combining a solid phase of powdered ingredients with a binder and dispersing it into a liquid called the "vehicle." Colorants are added by blending to produce a final product, which is applied to interior or exterior surfaces. Upon drying there is left a decorative and protective film. Most paints are brushed, rolled or sprayed onto surfaces. As a result, paint contains a wide variety of chemicals.

Solid Phase

In the first part of making paint, solid ingredients are combined. Titanium dioxide hides underlying surfaces and provides specular brightness. Other chemical solids -- such as aluminum oxide, silica and calcium carbonate -- serve as extenders. They provide bulk and thus keep costs low. Clays such as bentonite or kaolinite add body and modify flow properties. Diatomaceous earth reduces gloss. Zinc oxide bolsters whiteness.

Binder

A binder is a film-forming organic paint component that forms a matrix for coating longevity by strong adhesion to individual particles. The chemistry of the binder depends upon whether the paint is non-aqueous or latex. Non-aqueous paint binders may be oil-based or alkyd. Latex paints contain polymeric substances, such as polyvinyl acetate.

Liquid Phase

The liquid is also called the vehicle; it allows all the components of the paint to work together and to be applied properly across the surface. Much of the liquid phase of latex paints is water, while non-aqueous paints contain thinner, such as mineral spirits. Additional water or paint thinner may be added if a thinner coating is desired, covering more surface area per volume of paint. Thinning the paint usually makes it less strong.

Colorants and Miscellaneous Additives

Colorants are concentrated paint-coloring agents containing the color component of the paint. Generally, the color comes from insoluble pigment compounds. These colorants may be added in specific quantities at the end of manufacture to generate the desired shade according to a color chart.

Additional ingredients modify paint properties or change its purpose. Surfactant-a kind of detergent--improves application and gloss. Anti-foaming agents decrease bubbles. An anti-rust agent may be included to protect metal surfaces. Mercury compounds were once commonly added as a biocide. A drying agent-perhaps a long-chained metal carboxylate-is added to speed dry time. Co-solvents may be added to improve component stability and depress freezing. Finally, scent may be added to improve paint odor.

References and Resources:

Buildings: The Ingredients of Paint
State of Washington - The Department of Ecology: Paints and Coatings
Personal Experience: Paint Chemist